1. Field of the Invention
The present invention relates to a semiconductor device contained inside a package thereof, a method of manufacturing such semiconductor device, an adhesive material that is used in manufacturing such semiconductor device, and a method of producing this adhesive material. Particularly, the present invention relates to a semiconductor device in which an acceleration sensor for detecting acceleration in three dimensions is contained inside the package, a method of manufacturing such semiconductor device, an adhesive material that is used in manufacturing such semiconductor device, and a method of producing this adhesive material.
2. Background Information
In recent years, acceleration sensors have come to be widely used in various fields of industry, such as automobiles, robots, various precision equipments, etc. Particularly, the demand for semiconductor acceleration sensors using a MEMS (micro electro mechanical system) has dramatically increased, for it is small in size, light, inexpensive, and can be expected to operate accurately and reliably.
There is a type of semiconductor acceleration sensor which detects acceleration by using the piezoresistive effect, i.e., a phenomenon in which a resistance value changes in proportion to a generated stress. This type of semiconductor acceleration sensor usually has a structure in which a semiconductor chip that forms a portion of a sensor (hereinafter such semiconductor chip will be referred to as a sensor chip) is contained inside a package that is comprised of a ceramic material.
A sensor chip using the piezoresistive effect, for instance, has a structure in which a spindle body placed in the center thereof is supported by four flexible beams, each of which has one end fixed to a square fixing portion. These beams each have piezoresistive elements attached thereto, and a Wheatstone bridge circuit can be obtained by connecting these piezoresistive elements to each other via wiring patterns.
In a semiconductor acceleration sensor having such sensor chip, the beams will bend due to the stress generated by the inertial movement of the spindle body when there is a change in speed. At the same time, the piezoresistive elements attached to the beams will also bend. Due to such bending, the resistance value of each piezoresistive element will change, resulting in a change the resistance balance in the Wheatsone bridge. Acceleration can be detected by measuring such change in resistance balance as a current change or a voltage change.
Generally, the sensor chip as described above may be fixed to a cavity inside the package by means of an adhesive material such as an epoxy resin, Pyrex™ glass 7744, kovar, etc., (e.g. patent reference 1 (Laid-Open Japanese Patent Application No. 6-160423) and patent reference 2 (Laid-Open Japanese Patent Application No. 9-316166)).
However, the adhesive material, such as epoxy resin, Pyrex glass 7744, kovar, etc., has a higher elastic modulus than a material such as silicone resin, for instance. Therefore, when such material is used in order to mount the sensor chip on the package, there is a possibility that the impact resistance of the semiconductor acceleration sensor may deteriorate.
One measure for resolving such problem might be to use a resin having a comparatively low elastic modulus, such as silicone resin, fluorine resin, etc., as the adhesive material, instead of using the above described material having a comparatively high elastic modulus.
However, a resin having a comparatively low elastic modulus usually has a large coefficient of thermal expansion (CTE). Therefore, when there is a temperature change, the adhesive portion between the sensor chip and the package may expand/shrink to a considerable extent. This may impart a comparatively large stress to the sensor chip, and may result in a large amount of deformation in the sensor chip. As a result, the electrical characteristics of the piezoresistive elements attached to the sensor chip may change, which will lead to the sensor chip not being able to detect acceleration accurately.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved semiconductor device, an improved method of manufacturing a semiconductor device, and improved adhesive material and method of producing an adhesive material used in manufacturing a semiconductor device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.